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                <blockquote>
<p>本文转自：<a href="http://www.php20.cn/article/sw/高并发/244" target="_blank" rel="noopener">http://www.php20.cn/article/sw/%E9%AB%98%E5%B9%B6%E5%8F%91/244</a></p>
</blockquote>
<h2 id="1-CDN代理层"><a href="#1-CDN代理层" class="headerlink" title="1. CDN代理层"></a>1. CDN代理层</h2><blockquote>
<p>在高并发下，为了解决带宽问题，全站必须做前后端分离操作，所有前端资源都可进行CDN代理，进行缓存静态资源，分散服务器带宽压力。</p>
<p>同时，app端，小程序端等本地资源无需担心这个问题。</p>
</blockquote>
<h2 id="2-防火墙层"><a href="#2-防火墙层" class="headerlink" title="2. 防火墙层"></a>2. 防火墙层</h2><p>1、在大多数并发情况下，都可能存在恶意请求，例如CC，DDOS攻击，通过脚本，1秒请求100次，1000次请求，我们可直接认定该请求以及请求后的客户端为恶意请求，拒绝该客户端请求。</p>
<p>2、由于数据网络的特殊性，可能存在多个手机网络共用一个ip的情况，理论上不能直接封停ip，而是需要根据该次请求客户端附带的其他信息(ua标识)来用于拒绝。</p>
<p>3、同时，对已登录用户做好限流，同一个用户，理论上一次性不可能超过10次接口请求(静态资源不算)</p>
<p>4、防火墙其他规则可执行研究</p>
<h2 id="3-网关层"><a href="#3-网关层" class="headerlink" title="3. 网关层"></a>3. 网关层</h2><blockquote>
<p>网关层可以和防火墙层可以为同一个逻辑，通过防火墙后，进行请求调度，例如 Nginx 负载均衡。网关层需要对请求进行调度，将请求通过轮询/空闲判定，权重判定等方式，把请求分配到多台服务器，进行服务器压力分担。</p>
</blockquote>
<p>==注意：所有内部通信，最好都为内网环境，降低带宽压力，以及提升相应==</p>
<h3 id="4-微服务层"><a href="#4-微服务层" class="headerlink" title="4. 微服务层"></a>4. 微服务层</h3><blockquote>
<p>微服务层是个概念性层，可要可不要，在微服务层，可对请求进行服务分散，在大压力情况下，有必要关闭一些微服务应用进行服务降级，保证主要服务的运行。</p>
</blockquote>
<p>例如：在淘宝双十一时，关闭了退款通道。</p>
<p>例如：当商城高并发时，关闭查看历史订单功能，关闭小游戏功能，等等。</p>
<p>微服务层可能会出现<code>分布式事务</code>问题，有一定的难度。</p>
<h2 id="5-进程模型优化"><a href="#5-进程模型优化" class="headerlink" title="5.进程模型优化"></a>5.进程模型优化</h2><blockquote>
<p>在传统 php-fpm 模型中，单进程作为同步阻塞模型，一个进程在同一时间只能处理一个请求，当出现io阻塞后，进程会一直被请求占用，直到io结束，如果需要提升并发，就必须增加进程数，增加进程数意味着cpu调度进程压力增大，导致cpu耗费资源加大。</p>
<p>通过 swoole 的多进程多协程并发模型，一个进程可同时处理多个请求，cpu只要调度少量的进程，即可实现处理更多的请求。</p>
</blockquote>
<h2 id="6-PHP解释层优化"><a href="#6-PHP解释层优化" class="headerlink" title="6. PHP解释层优化"></a>6. PHP解释层优化</h2><blockquote>
<p>在正常php-fpm中，php运行需要经过以下几个步骤：加载php文件-&gt;逐行解释-&gt;运行 一个php项目，一次请求可能存在10-50个文件(laravel框架更多)，每次请求进来，都需要重新引入文件，加载文件，导致<code>磁盘io负载</code>暴涨。</p>
</blockquote>
<p>==我们可以通过opcache对文件进行解释加载进内存，二次请求不会再去重新加载php文件如果不想做opcache，也可直接将项目代码放进内存文件系统中，也可通过swoole、wokerman等常驻内存框架提升一点速度，也可实现一次加载永久存在的目的，提升性能。php作为服务端语言，主要瓶颈在于io，在高并发下，这些优化也是有限的。没有过于追求的必要。==</p>
<h2 id="7-服务器缓存层"><a href="#7-服务器缓存层" class="headerlink" title="7. 服务器缓存层"></a>7. 服务器缓存层</h2><blockquote>
<p>理论上，一次接口请求进来，非即时性查询，高频请求，都必须先经过缓存层,通过缓存减小数据库压力。</p>
</blockquote>
<p>例如：商品缓存，文章缓存等等。</p>
<p>==注意：为了避免缓存穿透，需要对所有缓存定时更新期限，并且将失效时间进行错开，确保不会出现一瞬间所有缓存失效，导致请求全部进入数据库。为了避免内存溢出,，需要对所有缓存字段进行管理，做失效时间，定时删除垃圾数据。==</p>
<h2 id="8-并发锁相关"><a href="#8-并发锁相关" class="headerlink" title="8. 并发锁相关"></a>8. 并发锁相关</h2><blockquote>
<p>在并发下，如果对数据准确度有一定要求的话，将涉及到并发锁功能。</p>
<p>在MySQL中，MyISAM引擎虽然插入、查询性能高，但是它使用表锁，如果在大表更新情况下，将造成锁表，导致全服务器请求都将锁住等待，所以MyISAM不能用于大表更新等业务，只适合做日志记录。</p>
<p>同时，InnoDB支持事务，行级锁，在更新用户金额时，可使用InnoDB存储引擎的表存储用户金额，进行行级更新。</p>
<p>可查看：<a href="http://www.php20.cn/tag/33" target="_blank" rel="noopener">并发锁</a></p>
</blockquote>
<p>==注意：InnoDB虽然作为行级锁，但是也需要考虑操作表的单位数量，例如用户金额，理论上只有用户自身请求，并发量并不大，就算是锁表，也不会影响到其他用户的操作。(如果你非得用脚本点1000下下单，那也是你牛逼，给你锁表1000秒也是你自找的)。但如果是商品库存，将不能直接使用 InnoDB 实现行锁，原因是该数据可能会被成千上万的用户进行请求，当锁住后，其他请求都需要等待，极度影响用户体验。==</p>
<h2 id="9-异步队列压力"><a href="#9-异步队列压力" class="headerlink" title="9. 异步队列压力"></a>9. 异步队列压力</h2><blockquote>
<p>如果是高并发场景为瞬时并发,例如商品秒杀只有1秒,其他时间都为低流量请求情况,可通过队列转为异步处理,前端等待n秒获取异步结果<br>通过异步队列,可分散瞬时并发带来的压力,使得服务器不会瞬间宕机导致出错. </p>
</blockquote>
<p>==注:异步队列处理缺点在于用户不能即时获取到结果,但是一般不会太久,如果超出3秒,可直接丢弃该请求,直接给用户返回失败.== </p>
<p>==如果是不需要获取结果的,例如插入日志,发送邮件,可直接使用队列==</p>
<h2 id="10-数据库主从"><a href="#10-数据库主从" class="headerlink" title="10. 数据库主从"></a>10. 数据库主从</h2><blockquote>
<p>为了避免数据库压力过大,可对数据库做主从环境,非主要数据全部从从数据库读取,减少主数据库压力.</p>
</blockquote>
<p>可查看: <a href="http://www.php20.cn/article/236" target="_blank" rel="noopener">关于mysql集群主从服务器搭建</a></p>
<p>==注意:需要注意主从同步数据延迟问题,以及主从断开后数据恢复问题==</p>
<h2 id="11-数据库分表"><a href="#11-数据库分表" class="headerlink" title="11. 数据库分表"></a>11. 数据库分表</h2><blockquote>
<p>可查看:<a href="http://www.php20.cn/article/189" target="_blank" rel="noopener">mysql分表详解</a></p>
<p>通过对数据库进行分表,降低单表锁表情况,分散单表查询压力.</p>
</blockquote>
<h2 id="12-数据库索引优化"><a href="#12-数据库索引优化" class="headerlink" title="12. 数据库索引优化"></a>12. 数据库索引优化</h2><blockquote>
<p>通过优化数据库索引,保障查询时命中索引,减少 临时表</p>
<p>可查看: <a href="http://www.php20.cn/article/209" target="_blank" rel="noopener">Mysql索引优化</a></p>
</blockquote>
<h2 id="13-尽量不要出现报错"><a href="#13-尽量不要出现报错" class="headerlink" title="13. 尽量不要出现报错"></a>13. 尽量不要出现报错</h2><blockquote>
<p>虽然 notice 报错不会影响服务正常运行,但是一次报错,涉及到了php底层的错误拦截机制,会影响非常多的性能,所以尽量不要出现任何报错.</p>
<p>解决任何可能存在的代码报错情况,改用自己的方式拦截,记录日志. </p>
</blockquote>

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